The present invention is directed to a device for aligning plates or sheet-shaped workpieces as they are used in an infeed station of a package producing machine, which device includes a feeding table provided with a horizontal passage allowing a sheet or workpiece to travel through, one-by-one, and having a length, which, in the travelling direction, covers the distance at least equal to the length of the maximum size of the sheet being process and has two pairs of rollers, with each pair having a lower driven roller and an upper roller, the lower driven roller being positioned beneath the passage and serving as a support for the sheet and the upper roller being situated on top of the passage and being mounted for movement between a rest position without exerting pressure on or contact with the sheet and a second position in which it will urge the sheet toward the lower roller, the axis of rotation of the lower roller being substantially perpendicular to a direction of travel of the sheet, while the upper roller can be moved to a position forming a slight angle with the axis of the lower roller to cause the sheet to be urged laterally against a guiding or aligning edge of the feeder table.
In machines for printing workpieces formed by sheets of pasteboard or corrugated cardboard and in machines for cutting such workpieces, the workpieces are generally loaded as successive piles into an infeed station. In many cases, the piles are neither exactly straight vertically nor properly centered on the machine axis. For this reason, after the successive separation of the workpiece, either from the top or the bottom of the pile, the various workpieces are fed individually into a device for a lateral and frontwise alignment in order to have them accurately positioned with regard to either gripper bars, which are fitted on a pair of endless chains and are designed to carry the workpiece individually through the subsequent cutting and waste stripping stations of the die-cutting machine or to infeed rollers of, for instance, a flexographic printing station.
For this purpose, such machines generally include an infeed station with a feeder table provided with a passage, which has a length in the sheet travelling direction to be at least equal to the maximum size of the sheet to be processed. After the workpiece arrives on the feeding table, the workpiece is stopped by aligning front lays or stops. Thereupon, an upper and lower roller acting pairwise will nip the sheet edge and, owing to their rotary motion, pull it sidewise against a lateral guiding surface or ruler. The axis of the two rollers is arranged essentially perpendicular to the sheet travelling direction. When rotated, the lower roller is held in a fixed horizontal plane, whereas the upper roller acts as a free wheel and may take a first position, in which it is not in pressure contact with a sheet, and a second position, in which it presses the sheets against the lower roller.
A major shortcoming of such a device for lateral and frontwise alignment is that it imposes a full standstill or stopping of each sheet. Such a standstill, which is followed by further conveyance, not only requires relatively complicated control means, but also is hardly compatible with the present, unceasingly increasing production speeds, since a standstill necessitates augments of the duration of the aligning operation.
Moreover, it is ensued from prior art that continuous aligning of travelling sheets can be achieved by means of a pair of rollers, of which the lower one is driven in the travelling direction, whereas the upper one acting as a free wheel is arranged slightly obliquely with regard to the travelling direction. However, the upper roller is subjected to a premature wear, since not only is it vulcanized and not driven, but also has a tendency to leave a furrow-like compression on a sheet during its first contact with the roller when at a standstill. In such a case, the sheets are generally pushed from behind by auxiliary means.
In addition, the aligning devices, known up to now, have the drawback of requiring two reference lines on the sheet, one on the rear edge enabling the gripper bars to seize it in the cutting, creasing and embossing station, and the other on the front edge for rollers of a printer, which way of handling may necessitate a 180.degree. inversion or turning over of the sheet when it passes from the printing device to the cutting unit.